1. Field of the Invention
The present invention relates to a projector-type vehicle headlamp and, in particular, relates to a vehicle headlamp which forms a distribution light pattern for a low beam.
2. Description of the Related Art
In general, a projector-type vehicle headlamp is configured such that a projection lens is disposed on an optical axis extending in the longitudinal direction of a vehicle, a light source is disposed on the rear side of the rear side focal point of the projection lens, and the light from the light source is reflected by a reflector toward the optical axis. When a distribution light pattern for a low beam is formed using the projector-type vehicle headlamp, the headlamp is configured such that apart of the light reflected from the reflector is shielded by a shade disposed so that the upper end edge thereof extends near the rear side focal point of the projection lens, thereby forming a predetermined cutoff line at the upper end portion of the low beam distribution light pattern.
JP-A-2002-42516 discloses a projector-type vehicle headlamp having the aforesaid shade. JP-A-2002-42516 discloses a projector-type vehicle headlamp in which a light source is movable between a reference position located near the optical axis thereof and moving positions located in the left, right and lower directions with respect to the reference position, thereby changing the shape and the luminance distribution of a low beam distribution light pattern.
Further, JP-A-2004-327187 discloses a projector-type vehicle headlamp in which a shade is movable, and when the upper end edge thereof is moved slightly downward, the cutoff line of a low beam distribution light pattern is moved slightly upward, thereby improving the visibility at a distant place on the road surface in the forward direction of a vehicle.
By employing the lamp disclosed in JP-A-2004-327187, it is possible to selectively switch between a low beam distribution light pattern suitable for normal driving and a low beam distribution light pattern suitable for high speed driving.
Such selective forming of the distribution light pattern may be obtained by moving the light source instead of moving the shade. However, if one tries to employ the lamp structure disclosed in JP-A-2002-42516, it is difficult to provide selective forming of the distribution light pattern due to the following reasons.
That is, since the vehicle headlamp described in JP-A-2002-42516 is configured to move the light source in a direction perpendicular to the optical axis thereof, the shape and the luminance distribution of the low beam distribution light pattern can be changed, but the degree of light convergence cannot be changed.
Further, the vehicle headlamp described in JP-A-2002-42516 employs the reflecting surface of a reflector which is designed based on an assumption that the light source is located at the reference position, even though the light source moves. Thus, it is not easy to set the low beam distribution light pattern to a desired distribution light pattern with a light source designed to be moved.
Thus, according to such lamp configurations, it is difficult to selectively form the low beam distribution light pattern suitable for the normal driving and the low beam distribution light pattern suitable for the high speed driving.